The present invention relates to a rotary drive apparatus, and in particular, to one having a pair of rotary elements which rotate about a common axis in start-and-stop cycles which are out of phase with each other.
In my U.S. Pat. No. 4,127,367 issued Nov. 28, 1978, there is disclosed a rotary fluid motor having a pair of start-and-stop rotary elements which are driven alternately in a forward direction under the influence of an external source of pressurized gas. The rotary elements are coupled to a rotary drive shaft in the motor by means of a spring drive connection which operates to "cushion" the torque which is applied to the drive shaft from the two start-and-stop elements, thus providing a substantially smooth drive connection between the elements and the drive shaft. The springs are subject to rapid metal fatigue and ultimately may lose some or most of their elasticity. When this occurs, the rotational movement of the drive shaft acquires more of the start-and-stop character of the driving rotary elements.
In the rotary fluid apparatus of the present invention, the rotary elements are coupled to the drive shaft by a fluid gradient which is formed in response to rotational advancement of the rotary elements with respect to the shaft. In the embodiment of the invention described herein, the drive shaft in the apparatus has, adjacent opposed shaft ends, angularly spaced vanes which are interspersed with angularly spaced vanes on associated rotary elements to form substantially sealed fluid chambers. Gas compression and expansion in alternate fluid chambers produced by relative rotational movement of the rotary elements with respect to the shaft acts to drive the shaft at a relatively constant velocity.
A general object of the invention is to provide a rotary fluid apparatus which overcomes performance and maintenance problems inherent in a rotary fluid motor having spring-like connections between its drive shaft and a pair of start-and-stop driving elements.
Another specific object of the present invention is to provide in a rotary fluid motor having a pair of start-and-stop rotary elements a compressible fluid drive connection between the rotary elements and a drive shaft in the motor.
Another object of the present invention is to provide a rotary fluid apparatus having a substantially constant velocity drive output.
These and other objects and features of the present invention will become more fully apparent when the following detailed description of a preferred embodiment of the invention is read in connection with the accompanying drawings.